The invention is concerned with a multi-speed shifting gear, and to specific, a two directional two-speed shifting gear of middle axle all kinds of pedal cycles.
It is very common that the middle axle of a typical pedal cycle, such as a bicycle, possesses no function of changing speed. To offer a pedal cycle a speed changing function, normally a speed changing set should be attached to it, for example, a kind of speed changing set made of two to five pieces of chainwheels with different sizes is montaged on the middle axle of a bicycle. As it is known that with this kind of speed changing set, the speed changing of the bicycle may be realized by selectively changing the size of the chainwheel of the driven chain. However with such mechanism, the rotating direction of the middle axle may be restrained only in one direction.
Previously, the inventor of this invention had designed a two-way-driven 2 speed free wheel (Utility model patent No. 8520275, Chinese Patent Office) and a two-way-driven 3 speed free wheel (Invention patent No. 90105171.3, Chinese Patent Office) , which are capable of gear-changing as well as motion transmission. Also, both structures can cause a bicycle to go forward whether pedalling in the same direction or backward, and each can be installed on ordinary pedal cycles and fitness bikes as a gear changing mechanism.
The purpose of the invention wherein the article provides a speed shifting gear for the middle axle, which is characterized by having a simple construction, and especially having the possibility of changing speed through pedalling in two directions.